mx.kronos.net has no NS records.
NS records for this zone are defined at kronos.net.
NS records for this zone are defined at kronos.net.
Question and response
Question
dig mx.kronos.net. NS
Answer
The response has no answer records.
Authority
kronos.net. 900 SOA ns1-auth.kronos.net. hostmaster.kronos.net. 70421 3600 1800 604800 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0